Since man first touched the moon and brought pieces of it back to Earth, scientists have thought that the lunar surface was bone dry. But new observations from three different spacecraft have put this notion to rest with what has been called "unambiguous evidence" of water across the surface of the moon.

The new findings, detailed in the Sept. 25 issue of the journal Science, come in the wake of further evidence of lunar polar water ice by NASA's Lunar Reconnaissance Orbiter and just weeks before the planned lunar impact of NASA's LCROSS satellite, which will hit one of the permanently shadowed craters at the moon's south pole in hope of churning up evidence of water ice deposits in the debris field.

The moon remains drier than any desert on Earth, but the water is said to exist on the moon in very small quantities. Finding water on the moon would be a boon to possible future lunar bases, acting as a potential source of drinking water and fuel.

Three Spacecraft:

Chandrayaan-1, India's first-ever moon probe, was aimed at mapping the lunar surface and determining its mineral composition (the orbiter's mission ended 14 months prematurely in August after an abrupt malfunction). While the probe was still active, its NASA-built Moon Mineralogy Mapper (M3) detected wavelengths of light reflected off the surface that indicated the chemical bond between hydrogen and oxygen — the telltale sign of either water or hydroxyl.

Because M3 can only penetrate the top few millimeters of lunar regolith, the newly observed water seems to be at or near the lunar surface. M3's observations also showed that the water signal got stronger toward the polar regions.

Cassini, which passed by the moon in 1999 on its way to Saturn, provides confirmation of this signal with its own slightly stronger detection of the water/hydroxyl signal. The water would have to be absorbed or trapped in the glass and minerals at the lunar surface, wrote Roger Clark of the U.S. Geological Survey in the study detailing Cassini's findings.

The Cassini data shows a global distribution of the water signal, though it also appears stronger near the poles (and low in the lunar maria).

Finally, the Deep Impact spacecraft, as part of its extended EPOXI mission and at the request of the M3 team, made infrared detections of water and hydroxyl as part of a calibration exercise during several close approaches of the Earth-Moon system en route to its planned flyby of comet 103P/Hartley 2 in November 2010.

Deep Impact detected the signal at all latitudes above 10 degrees N, though once again, the poles showed the strongest signals. With its multiple passes, Deep Impact was able to observe the same regions at different times of the lunar day. At noon, when the sun's rays were strongest, the water feature was lowest, while in the morning, the feature was stronger.

"The Deep Impact observations of the Moon not only unequivocally confirm the presence of [water/hydroxyl] on the lunar surface, but also reveal that the entire lunar surface is hydrated during at least some portion of the lunar day," the authors wrote in their study.

The findings of all three spacecraft "provide unambiguous evidence for the presence of hydroxyl or water," said Paul Lacey of the University of Hawaii in an opinion essay accompanying the three studies. Lacey was not involved in any of the missions.

The new data "prompt a critical reexamination of the notion that the moon is dry. It is not," Lacey wrote.

Where the water comes from

Combined, the findings show that not only is the moon hydrated, the process that makes it so is a dynamic one that is driven by the daily changes in solar radiation hitting any given spot on the surface.

The sun might also have something to do with how the water got there.

There are potentially two types of water on the moon: that brought from outside sources, such as water-bearing comets striking the surface, or that that originates on the moon.

This second, endogenic, source is thought to possibly come from the interaction of the solar wind with moon rocks and soils.

The rocks and regolith that make up the lunar surface are about 45 percent oxygen (combined with other elements as mostly silicate minerals). The solar wind — the constant stream of charged particles emitted by the sun — are mostly protons, or positively charged hydrogen atoms.

If the charged hydrogens, which are traveling at one-third the speed of light, hit the lunar surface with enough force, they break apart oxygen bonds in soil materials, Taylor, the M3 team member suspects. Where free oxygen and hydrogen exist, there is a high chance that trace amounts of water will form.

The various study researchers also suggest that the daily dehydration and rehydration of the trace water across the surface could lead to the migration of hydroxyl and hydrogen towards the poles where it can accumulate in the cold traps of the permanently shadowed regions.

It only makes sense. The moon is orbiting the Earth, and would thus experience the same processes that gave the Earth water if we are correct about most of the water coming from asteroids in the early history of Earth. I always figured that the Moon just didn't have enough gravity to contain it in an atmosphere/didn't attract as many asteroids/whatever.

It only makes sense. The moon is orbiting the Earth, and would thus experience the same processes that gave the Earth water if we are correct about most of the water coming from asteroids in the early history of Earth. I always figured that the Moon just didn't have enough gravity to contain it in an atmosphere/didn't attract as many asteroids/whatever.

More than enough asteroids make it onto the moon. I believe the lack of an atmosphere is the reason for that.

http://www.space4schools.co.uk/pages/lunar/moon.jpg
I'm fairly sure all those craters are from asteroids.

Also, the moon has enough gravity. If a person can sorta walk along the surface, then water should stay on the surface, too. It's not just going to float away.

Low qualities in sunlight and higher quantities just after lunar morning really suggest an accumulation at the South Pole. LCROSS is hugely important, this could make lunar colonization more viable than ever.

There's water everywhere basically.
On Mars there enough (frozen) water to fill the entire of Mars with 11m of liquid water.
Lots of satellites have vapor or frozen water.
Besides, there's the hipothesis that the Moon is a big part of Earth, who got collisioned into by another planet.